The present invention relates generally to a disc pack assembly for use in disc drive storage systems and external servo writers, and more particularly but not by limitation, to a disc pack assembly that can be assembled outside of the disc drive or servo writer and is configured to maintain concentric alignment between one or more discs and a hub during handling.
Modern computers employ various forms of storage systems for storing programs and data. These storage systems include disc drive systems that operate under the control of a computer to record information and/or retrieve recorded information on one or more recording discs. Such disc drives include hard disc drives which employ recording discs that have magnetizable recording material, optical disc drives which employ recording discs that have optically readable recording material, magneto-optical disc drives which employ recording discs that have optically readable magnetizable recording material, and the like.
Conventional disc drive systems typically include one or more recording discs (disc stack) supported for high speed rotation on a rotary spindle that is driven by a motor. The spindle can be a rotatable shaft, or sleeve surrounding a shaft, of a fluid dynamic bearing cartridge, for example. The rotatable spindle defines the core of the stack, is cylindrical in shape and serves to align the disc or discs around a common axis. Reading and/or writing heads are positioned adjacent surfaces of the discs for reading data from and/or writing data to circular concentric data tracks.
A disc clamp is used to secure the disc or discs to the spindle. To assure that proper registration of the discs for reading and writing purposes can be achieved, the disc clamp must secure the discs to the spindle to prevent them from dislodging and moving in the axial or radial direction once mounted to the spindle. Thus, the discs must be protected from non-operational shocks that can occur during handling of the disc drive, installation of the disc drive into a computer, and during transport and use of the computer. Additionally, it is desirable that the discs be mounted without deforming the discs, which may adversely affect the reading and writing performance of the heads. Finally, it is desirable that the height required by the disc clamp to mount the discs to the spindle be minimized to meet the never-ending demands for smaller and shorter disc drives.
Current systems utilize a disc clamp to secure the discs in place on the spindle. Conventional disc clamps are available in various configurations. One known type of disc clamp uses screws passed through a circular plate and into tapped openings in the spindle to provide the clamping force that secures the discs in place. Unfortunately, the circular plate and screws undesirably add height to the disc stack. In addition, the individual screws produce localized stresses in the discs, which may undesirably distort the shape of the disc.
A second known type of disc clamp includes a bell-shaped part that operates as a spring. Typically, screws are passed through openings in the center of the bell-shaped part and into a tapped opening in the spindle. Unfortunately, this design requires substantial spindle height. In addition, attaching the screws at the center of the spindle causes the bell-shaped part to flatten as the screws are tightened. The edges of the bell-shaped part which contact the disc during tightening move across the surface of the disc in a radially outward direction. The movement of the disc clamp with respect to the disc causes the disc to undesirably distort into a conical shape, and produces a radial load on the disc.
A third known type of disc clamp is a heat-shrink ring which is attached to the top of the hub without the use of screws. This type of disc clamp is often referred to as a shrink-fit disc clamp. A ring is heated so that it expands and the inner diameter of the ring is greater than the outer diameter of the hub. A tool is then used to transfer the heated ring to the top of the disc stack and to apply a clamping force to the heated ring. The clamping force is maintained on the ring as it cools resulting in the application of a substantially uniform axial load to the discs. Unfortunately, mounting of the discs to the drive using such a shrink-fit disc clamp can be complicated and problems with slippage of the ring on the spindle can arise.
As mentioned above, the discs used in disc drives generally include circular data tracks which extend circumferentially around each disc. The boundaries and centerlines of each data track are defined by radially extending servo tracks that contain servo information. Disc drives utilize servo systems to control the position of a read/write head relative to the data tracks using the servo information stored in the servo tracks. As a head moves over a surface of a disc, the head reads the servo information and produces an output signal that indicates its position relative to the servo tracks. The output signal is demodulated and compared with a reference position signal relating to a desired head position to produce a position error signal (PES). The PES is provided to a servo controller that produces a control signal which is used to control an actuator mechanism of the disc drive or spin-stand to move the head toward a desired data track. Once the head is positioned over the desired data track, the servo system allows the head to follow the track using the servo information.
The servo tracks are typically written after the discs have been mounted to the spindle of the disc drive using the disc clamp. These xe2x80x9cpost-writtenxe2x80x9d tracks are substantially concentric with the axis of rotation of the disc on which they are written, since the axis of rotation remains constant from when the servo information is written to when the servo information is used to perform track following. However, uncontrolled factors such as bearing tolerances, spindle resonances, displacement of the disc due to non-operational shocks, and the like, tend to introduce errors in the location of the servo information. As a result, each track is typically not perfectly concentric with the axis of rotation of the disc, but rather exhibits certain random, repeatable variations which are sometimes referred to as repeatable runout (RRO). This slight misalignment is exhibited in a periodic PES, which can be compensated for using conventional techniques.
There is a continuing trend in the disc drive industry to provide successive generations of disc drive products with ever increasing data storage capacities and data transfer rates. Because the amount of disc surface available for the recording of data remains substantially constant (or even decreases as disc drive form factors become smaller), substantial advancements in areal recording densities, both in terms of the number of bits that can be recorded on each track as well as the number of tracks on each disc (measured as tracks per inch or TPI), are continually being made in order to facilitate such increases in data capacity. One way to improve storage capacities is to improve the writing of the servo patterns on the discs.
To that end, servo information is written on the discs prior to their installation in a disc drive using highly precise servo writers. These xe2x80x9cpre-writtenxe2x80x9d tracks can result in a potential increase in the TPI of the disc. Unfortunately, disc drives incorporating discs having these pre-written tracks cannot realize an increase in recording capacity because the encountered RRO is too large to be compensated for using standard techniques. The large RRO is the result of a tremendous eccentricity that exists between the data tracks and the new axis of rotation of the discs that have been installed in the disc drive using conventional disc clamping methods, such as those discussed above.
There exists a never-ending demand for improvements to disc drives performance. To that end, it would be desirable to provide a disc pack assembly that provides substantially uniform axial clamping loads to the discs while avoiding the problems of the prior art mentioned above.
The present invention relates to a disc pack assembly for use in a disc drive storage system or external servo writer that is configured to maintain concentric alignment between one or more discs and a hub during handling. The disc pack assembly generally includes a disc support having an annular shoulder, a disc supported on the annular shoulder, and a hub top. The hub top includes a spindle mount portion, a ring mount portion and an annular clamping flange. The spindle mount portion is mountable to a rotatable spindle of a motor of a disc drive or an external servo writer. The ring mount portion is positioned in interference-fit engagement with the disc support for attachment thereto. The annular clamping flange applies an axial force to the disc to secure the disc between the clamping flange and the annular shoulder.
The present invention facilitates the assembly or partial assembly of the disc pack outside of a disc drive or an external servo writer while providing concentric alignment between one or more discs and a hub during handling. Due to this configuration, the disc pack assembly can have discs with pre-written servo tracks that, when mounted to a spindle of a disc drive, are more concentrically aligned with the axis of rotation of the spindle as compared to when prior art clamping methods are used to mount the pre-written discs to the spindle of the disc drive.
Other features and benefits that characterize embodiments of the present invention will be apparent upon reading the following detailed description and review of the associated drawings.